Help with hacking

Hello, i know this is my first post, but ive been using this site quite a bit lately and finally decided to sign up, but now i ran into a problem, for some odd reason after i rooted my phone it was woking perfectly, and i could type in su to the terminal and it would work, but now it says permission denied after i made a backup using nandroid, i have a backup of my nand, and apps and music, so i dont mind wiping it, but can someone help me? cause i was trying to install busybox to get a theme on my phone.

wow, ok easy fix, all i had to do was click on the superusers permission app and click on all the little things in it, and then it would let me use the su and gave me permission, thanks for your help though